1. Field of the Invention
The invention is related to fuel valves for a fuel flow injection circuit into a turbojet, or more generally into an aircraft engine. The valve is intended to be inserted in a servocontrol loop controlling the fuel flow directed towards the injectors of an aircraft engine.
2. Prior Art
Fuel valves are well known in the state of the art, and enable to adjust the section of the fuel passage and consequently to adjust the flow towards the engines. For example, this type of valve is known in patent FR 2 747 174 deposited by the SAMM (Socixc3xa9txc3xa9 d""Application des Machines Motricesxe2x80x94Driving Machines Application Company) for a hydraulic distributor for aircraft servocontrol. A distributor of the valve type described in this patent comprises a plug mounted free to rotate inside a fixed bushing housed in a body in which an annular element is inserted between the plug and the bushing. The plug comprises an opening which more or less coincides with an opening in the bushing in which the plug is free to rotate. Rotating the plug controls the section of the fuel passage and therefore the fuel flow. In valves controlled by an electrohydraulically servocontrolled delivery pump, the plug is rotated by a hydraulic regulation system in which the regulation fluid is composed of pressurized fuel.
The advantages of this type of fuel valve are well known, and particularly there is no longer any need to demonstrate its reliability considering the number of years during which it has been in use. However, there are disadvantages of valves regulated by a fuel powered electrohydraulically servocontrolled delivery pump, particularly because more fuel is necessary at the pump to supply regulation control devices, particularly due to the fact that regulation control devices must operate when the flow is at its lowest level. This oversizing of the pump and the weight of the fuel and regulation devices are expensive in terms of weight.
These devices may become seized if the fuel is polluted, which increases the risk of failures. To avoid the risk of the fuel freezing in regulation devices when the aircraft is at a high altitude, the fuel must be heated before it is allowed to enter the regulation devices. If the pump is oversized to maintain a satisfactory flow for regulation devices, the heat exchanger heating the fuel must be sized accordingly which increases the weight. The valve cannot be tested unless the valve is pressurized, which means that the aircraft engines are started up. Finally, when the valve is replaced, special care is necessary in the workshop to prevent foreign bodies from entering the valve, which in practice means that the valve cannot be quickly replaced on line.
Patent application FR 72 32411 deposited on Sep. 13, 1972 with a priority claim over application U.S. Pat. No. 208,249 on Dec. 15, 1971 describes a valve with a spherical closer 20. This closer 20 consists of a sphere in which a through cylinder is formed.
An engine 84 located outside the valve body 12 drives the closer 20 in rotation through a motor shaft 86, a reduction gear external to the body 12 and an output pinion 78. The output pinion 78 engages on a toothed sector 60 connected to the closer. The path of the liquid passing through the valve follows a trajectory along a line located in a plane perpendicular to the axis of rotation of the closer. The outside of the valve is sealed by seals 26, 28 and a Teflon add-on part 30.
It is well known that a seal cannot be made between two parts that move with respect to each other unless pressure is applied to the mobile part, which requires a greater torque on the mobile part.
The valve according to the invention operates on electrical energy rather than hydraulic energy.
Consequently, there is no longer any risk of pollution of the fuel causing failures, nor is there any need for heating of the fuel which reduces the exchanger weight and globally improves the reliability of the device according to the invention. Eliminating fuel as the driver vector can reduce the weight necessary for the function performed by the valve regulation devices and therefore the weight of the turbojet is reduced. A reduction in the weight is also achieved by the smaller size of the pumping systems in the turbojet fuel circuits. As mentioned above, this size depends on the flow necessary to activate the hydraulic subassemblies when the turbojet is in operation at very low speed and therefore when the pump outputs low flows. Therefore, the lack of any flow necessary to actuate the valve according to the invention can improve the sizing of the pumping system, in terms of weight. Therefore, the overall weight of the turbojet is reduced. The valve according to the invention may also be pre-adjusted so that it outputs exactly the turbojet ignition flow, or the heating flow when the jet engine has a heating system, for example for Air Force engines, even before the fuel passes through the valve. Consequently, the performances of the turbojet in terms of capacity and ignition speed are very much improved. The valve according to the invention may be tested without the input of any hydraulic energy, which means that it can be tested without the need to turn the turbojet. Therefore, maintenance of the turbojet is very much improved. Finally, as mentioned above, the valve according to the invention can be replaced and tested without the need to start up the jet, so that the valve according to the invention becomes a line replaceable element.
In summary, a valve according to the invention has better availability in use and in service, is safer and more reliable, has lower maintenance and ownership costs, improved maintenance, improved performances, and furthermore the weight of the valve control function is lower and it is more compact.
According to the invention, the valve is controlled using an electric motor assembly and a mechanical reduction gear with a large reduction ratio, the electric motor output shaft being input to one end of the reduction gear with the output of the reduction gear controlling the position of a distributor plug through a gear system, and the said distributor. In summary, the invention relates to a fuel valve with direct electrical control comprising:
a fuel distribution assembly comprising:
a fuel inlet opening
a bushing comprising a first opening
a mobile plug in the bushing comprising a second opening
a fuel outlet with an open section that depends on the overlapping area between the first opening in the bushing and the second opening in the plug
means of controlling the position of the plug in order to vary the value of the overlapping section between the first and second openings, the valve being characterized in that the means of controlling the plug position comprise the following, housed in a valve body communicating with the distribution assembly,
a brushless electric motor rotating around a shaft AAxe2x80x2, this motor driving a mechanical reduction gear assembly, this assembly comprising an input shaft and an output pinion or shaft from the reduction gear assembly, such that a motor rotation movement drives a movement of the plug and changes the overlapping areas of the first and second openings.
The fuel inlet opening is made according to a section with a fixed area and is perpendicular to the axis of rotation of the plug. Thus, the fuel inlet is parallel to the axis of rotation of the plug. The result is an opening located on a cylindrical wall of the plug centered on the axis of the plug. Therefore, the fuel output is perpendicular to the axis of the plug.
Note that an opening may be composed of several holes or slits in a wall. It is desirable that all holes in the plug that are combined to form the plug opening satisfy symmetry of revolution of the opening about an axis of rotation of the plug.
The same is true for openings in the bushing. Therefore, in general there will be at least two openings.
Although in the following example, the motor is a rotating motor and the plug is a rotating plug, there is no reason why the motor should not be a motor with axial movement driving a plug with axial or rotating movement. The motor is preferably equipped with redundant stators, for better operating safety. The motor rotor is preferably a single-piece rotor with sides parallel to the rotor axis, for example six or eight sides with a hexagonal or octagonal section. Preferably, the motor is equipped with means of determining the angular position of the rotor about its axis at any time, for example by magnets located on each side in which the flux varies a signal transmitted through one or several Hall effect sensors, for example laid out axially at the same height as the magnets.
The stator motor and the rotor housed in the valve body in communication with the distribution assembly is immersed in the hot pressurized fuel, which eliminates problems of sealing leaks between the plug and the motor.